Evolution and Ecology

Evolution Overview

• Definitions of Evolution

  • Descent with modification

  • Change over time

• Smallest Unit of Evolution

  • Populations, not individuals (individuals do not evolve)

• Key Figures in Evolution

  • Charles Darwin and Alfred Russell Wallace:

    • Developed the Theory of Evolution.

    • Previous theories lacked testable mechanisms.

Early Concepts of Evolution

• Jean Baptiste Lamarck

  • Proposed evolution via inheritance of acquired characteristics.

• Natural Selection

  • Proposed by Darwin and Wallace.

  • Tested and supported by extensive biological studies.

Evidence for Evolution

• Types of Evidence

  • Biogeography

  • Fossils

  • Morphology (anatomical and biochemical evidence)

  • Genetic evidence

  • Ontogeny (development)

Biogeography

• Organism Similarity Across Continents

  • Explained by continental drift and plate tectonics.

    1. All continents were once part of Pangea.

    2. Pangea broke apart over 420 million years.

    3. Continents drifted into current positions.

• Endemism

  • Unique species found in specific regions (e.g., Hawaiian honeycreepers, prairie chickens).

Fossil Data

• Understanding Fossils

  • Fossils include preserved remains or impressions of organisms.

  • Found in sedimentary rock strata, with oldest layers at the bottom.

• Completeness of Fossil Record

  • Fossil record is rich but incomplete; not every organism is represented.

  • Fossils can be carbon-dated to estimate age.

Morphology and Comparative Anatomy

• Morphological Evidence

  • Homologous structures: similar due to common ancestry.

  • Analogous structures: similar due to environmental pressures, not common ancestry.

• Vestigial Structures

  • Structures that have lost their original function (e.g., human appendix, snake spurs).

Genetics and Ancestry

• DNA as Evidence of Ancestry

  • DNA is inherited and provides clarity on evolutionary lineage.

  • DNA analysis helps resolve previously unresolved evolutionary questions.

• Real-world Genetic Applications

  • DNA used in forensic cases (e.g., HIV case).

Developmental Biology

• Ontogeny and Phylogeny

  • “Ontogeny recapitulates phylogeny”: developmental stages reflect evolutionary history.

  • Shared developmental structures across species (e.g., pharyngeal pouches in embryos).

Natural Selection Principles

• Fundamentals of Natural Selection

  • Proposed by Darwin and Wallace, dissected by Ernst Mayr.

  • Based on five key observations leading to three key inferences.

    1. Populations grow exponentially but stabilize.

    2. Limited resources lead to competition.

    3. Variation in traits exists and is heritable.

• Definition

  • Differences in survival and reproduction due to traits within a population.

Modes of Natural Selection

• Types of Selection

  • Directional Selection: favors extreme phenotypes (e.g., male peacock tails).

  • Disruptive Selection: favors multiple extreme phenotypes.

  • Stabilizing Selection: favors intermediate phenotypes.

  • Sexual Selection: focuses on mating success.

Additional Evolutionary Mechanisms

• Mutation

  • Source of new genetic variation; does not directly change frequencies.

• Gene Flow

  • Movement into/out of populations; affects genetic variation.

• Genetic Drift

  • Random changes in allele frequencies, more impactful in small populations.

Species Concept and Speciation

• Defining Species

  • Biological species concept: groups can mate and create viable offspring.

  • Issues arise with asexual organisms and the fossil record.

• Types of Speciation

  • Allopatric Speciation: geographical separation leads to reproductive isolation.

  • Sympatric Speciation: occurs without geographical separation due to behavioral factors.

Ecology and Population Dynamics

• Population Definition

  • Group of individuals of the same species in a defined area.

• Demographics

  • Population size, age structure, density, and distribution.

• Carrying Capacity

  • Maximum population size that the environment can sustain.

• Reproductive Strategies

  • r-strategists: maximize offspring.

  • K-strategists: optimize offspring quality.

Community and Ecosystem Interactions

• Community Definition

  • A group of populations of different species in an area.

• Niche

  • Specific role and requirements of a species in its environment.

• Symbiosis

  • Interactions between species that can be positive, negative, or neutral.

• Key Species

  • Indicator species show community health; keystone species regulate community structure.

Ecosystem Dynamics

• Ecosystems

  • Complex networks of interacting biotic and abiotic elements.

  • Include producers (plants), consumers, decomposers, and detritivores.

• Energy flow within ecosystems and trophic levels.

• Biogeochemical Cycles

  • Movement of essential elements (e.g., hydrologic, nitrogen, phosphorus cycles)

  • Disruptions to these cycles can have significant ecological impacts.

Human Impact on Ecosystems

• Chemical Use in Agriculture

  • Pesticides like DDT can cause long-term ecological harm.

• Biomagnification

  • Toxic substances accumulate through trophic levels, affecting top predators.

• Global Warming and Greenhouse Gases

  • Rise in greenhouse gases threatens ecosystem balance.

Homologous Structures

• Structures that share a common ancestry but may have different functions (e.g., forelimbs of vertebrates: human arms, whale fins, bat wings). They indicate evolutionary relationships between species.

Vestigial Structures

• Anatomical features that have lost their original function through evolution (e.g., human appendix, wisdom teeth, and the pelvic bones in whales). These structures provide evidence of an organism's evolutionary past.

Analogous Structures

• Structures that serve a similar function but evolved independently in different species (e.g., wings of bats and insects). They arise from convergent evolution, not from a common ancestor.

Convergent Structures

• A type of evolutionary process where organisms from different evolutionary backgrounds develop similar traits due to similar environmental pressures or ecological niches (e.g., dolphins (mammals) and sharks (fish) both have streamlined bodies for swimming).

Types of Species Interactions

• Amensalism: A relationship where one species is harmed while the other is unaffected (e.g., trees that shade out smaller plants).

• Mutualism: An interaction where both species benefit (e.g., bees pollinating flowers while feeding on nectar).

• Parasitism: A relationship where one organism benefits at the expense of another (e.g., ticks feeding on mammals).

• Commensalism: An interaction where one organism benefits while the other is not affected (e.g., barnacles attaching to whales).

Niche

• The specific role and position an organism occupies in its environment, encompassing habitat, resource use, and interactions with other organisms (e.g., bees as pollinators).

Carrying Capacity

• The maximum number of individuals of a species that an environment can sustain indefinitely, based on resource availability (food, water, shelter, etc.).

Adaptive Radiation

• The process by which organisms diversify rapidly into a wide variety of forms to adapt to different environments (e.g., Darwin's finches on the Galápagos Islands).

Natural Selection Modes

• Intrasexual Selection: Competition among individuals of one sex (often males) for mates. (e.g., male deer fighting for access to females).

• Directional Selection: Favors one extreme phenotype over others, shifting the population mean (e.g., increase in size of beaks in finches during drought).

• Intersexual Selection: Selective pressure on one sex to choose mates based on certain traits (e.g., peahens selecting peacocks with the most elaborate tails).

• Stabilizing Selection: Favors intermediate phenotypes and reduces variation (e.g., birth weights of babies typically favoring average sizes).